1. Field of the Invention
This invention relates to recuperative heat exchangers of the formed plate type comprising a stacked plate arrangement with adjacent fluid passages in counterflow relation in the heat exchanger.
2. Description of the Prior Art
In numerous fluid flow processes it is necessary to either heat or cool one of the fluid streams. Various types of heat exchangers are used for this operation. One type often used is a plate type heat exchanger which may be formed of a multiplicity of plates stacked together and spaced in side by side relation. The spaces between adjacent plates provide flow paths adjacent each plate. Flow passages are arranged so that alternately one fluid stream passes through the passages on one side of the plate and the other stream flows on the other side of the plate.
In certain applications such as vehicle type heat exchangers, high performance and efficiency are demanded with an inherent low cost, small volume and light weight. Early attempts to accomplish these objectives have incorporated designs employing solid spacers or bars to provide the boundary junctures of the plates and to channel the hot and cold fluids to and from a counterflow section of the heat exchanger. Such designs are characterized by components which are costly to fabricate and to join together in the overall structure. Additionally, problems of structure integrity associated with thermal inertia incompatibility of the core elements due to the different size and thickness thereof were experienced. The high cost and other problems associated with such structures preclude their suitability for vehicle gas turbine use.
For a heat exchanger to be acceptable for use with small gas turbine designs, particularly for road-type vehicle applications, a minimum of labor in fabrication is mandatory to keep the costs within reason. In order to accomplish this, a heat exchanger must be designed which has a minimum of parts which can be easily formed and assembled. Additionally, the costs of the materials must be kept as low as practical, while maintaining design objectives of high efficiency, compactness, and lightness of weight.
A critical aspect of the heat exchanger core fabrication lies in the means for sealing the adjacent plates near the extremity of the core matrix. In the prior art typically plates have been reinforced and sealed by bars which increase the thermal transient stress in the heat exchanger due to their different size from the adjacent plates, and therefore, resulting different heat conductivity characteristics.
Thus, it may be seen that it is essential in the design of a heat exchanger for the vehicle gas turbine market to provide a recuperator that achieves thermal inertial compatibility between the elements of the core and parts attached to the core, in addition to being capable of long life and constructed of parts which may be fabricated and assembled with a minimum amount of labor.